Reconstruction of soft tissue defects is the major technical challenge for the craniofacial surgeon in the repair of cleft lip, hemifacial microsomia, and other disfiguring head and face congenital disorders. While free fat grafts are theoretically the ideal solution, their use has been plagued by graft resorption that results in suboptimal and disappointing outcomes. Fat graft resorption rates vary from 30-70%, requiring repetitive surgeries in an effort to reconstruct the child's face. Numerous clinical strategies have been used with inconsistent success to limit fat graft resorption. None of these approaches have yielded improved clinical outcomes; rigorous experimental analysis has not been conducted, and, most importantly, the mechanisms underlying fat graft resorption have never been investigated. We are conducting the first systematic investigation of the underlying biologic mechanism of fat graft resorption and mechanisms that might modulate resorption. Using an established animal model of human adipose tissue implanted into nude mice, our interdisciplinary research group employs immunochemical, molecular biological, and advanced imaging techniques to serially examine graft resorption and the molecular events that drive this process. Our first Aim is to systematically investigate the different clinical techniques available to harvest fat grafts, in order to determine the effects of graft handling on cell viability and biology. Our second Aim is to evaluate our leading hypothesis on fat graft resorption: determining the importance of an adequate blood supply to graft survival. We will investigate whether implanted grafts receive sufficient blood supply to sustain their survival, and then evaluate the effects of pro-angiongenic interventions. Our final Aim is geared to understand the role of adipocyte cell biology in fat graft resorption. Since adipocyte cell lineage differentiation status can change in implanted grafts, we will explore the contribution of this mechanism in graft failure. This project is the first systematic investigation of the mechanisms that underlie a major clinical obstacle in reconstructive surgery. Through this research project we hope to generate data that will seed larger, interdisciplinary research in this field.